Unraveling the Olmec rubber balls from El Manatí, Mexico: a technological and compositional analysis

Abstract

This work presents an analysis towards a description of the manufacturing technique of the Olmec rubber balls found at the offerings at El Manatí. The results present this procedure from the extraction of the Mesoamerican rubber from the Castilla elastica tree, discussing its composition and origin of the rubber balls analyzed towards the production of strips that are rolled to make the ball round form. This characterization was achieved through a series of imaging techniques (radiography imaging, UV-induced fluorescence imaging, and optical microscopy) and portable non-destructive and non-invasive analyses (XRF and FTIR) performed on the collection of archaeological rubber balls and compared with contemporary made rubber balls in the region near El Manatí. The methodology was complemented with laboratory chemical analytical techniques (13C NMR-MAS, FTIR, CEA, and GC-MS) applied to selected Olmec rubber microsamples. The new physical and chemical data obtained was also interpreted considering conservation science, to help understand the alterations and transformation processes that the balls have undergone since their recovery in the 1980s.